This invention relates to internal combustion valve seals and more specifically to valve seals located at a lower end portion of a valve guide, proximate to a combustion chamber.
In conventional overhead valve internal combustion engines, at least two valves reciprocate in timed alternation to provide intermittent communication between the intake and exhaust manifolds and a combustion chamber. The valves have valve stems which are commonly disposed in valve guides supporting axial motion in an engine head. Lubrication is provided to upper portions of the valve stems by a spray of lubricating oil within a valve cover disposed over the head, or by gravity flow from an associated rocker arm. Oil flows by gravity along the upper free end of the valve stem toward the valve head. Since temperatures in the combustion chamber may approach or exceed 1000.degree. Celsius, any lubricating oil exposed to these temperatures will vaporize and/or burn, leaving behind deposits which may interfere with proper sealing of the valves.
Seals between the valve stem and the valve guide have been commonly located in an upper end of the valve guide to restrict entry of oil into the combustion chamber. The upper end of the valve guide is distal to the combustion chamber, thereby distancing the seal from the intense heat of combustion.
As the valve axially translates between open and closed positions, the lower end of the stem rubs against a lower end of the guide. With the seal disposed in the upper region within the valve cover, little lubricant reaches a lower end of an overlapping region of the valve stem and valve guide. The seal is configured to supply a controlled flow of lubricant past the seal and along valve stem, providing some minimal protection against wear or scuffing of the valve stem against the guide without producing deposits of oil residue in the seating area. The resultant oil seal is an uneasy compromise which often results in valve scuffing of the valve stem.
A known technique of minimizing or eliminating valve scuffing is to locate the seal in a groove formed in a lower end of the valve stem. The seal seals against an inside diameter of the valve guide. However, because the valve moves within the valve guide, the seal must be located at an axial position along the valve stem which remains within the valve guide for the full range of valve travel so that the seal does not pass out of the valve guide. The resultant distance of the seal from the end of the valve guide may provide some opportunity for valve scuffing to occur. Additionally, the resultant reduction in cross sectional area produced by the valve decreases the strength of the valve stem.
It is also known to provide a seal formed of metal wire windings in a slot in a lower end of the valve guide. A wire seal is generally less effective at sealing than an elastomeric seal. Yet, elastomeric seals are more sensitive to heat when compared with wire seals.
Known engine valve seal arrangements do not readily accommodate the use of an elastomeric seal in an end of the valve guide most proximate to the combustion chamber.